FIG. 1 is a perspective view of a related art nuclear boiling water reactor (BWR) jet pump assembly 8. The major components of the jet pump assembly 8 include a riser pipe 3 and two inlet mixers 4 that insert into respective diffusers 2. Jet pump restrainer brackets are used to stabilize movement of the inlet mixers 4 and reduce movement of and leakage at slip joint 6 that exists at the interface between inlet mixers 4 and diffusers 2. One type of movement is Flow Induced Vibration, or FIV, that causes slip joint leakage due to high-velocity flows in and around assembly 8. Restrainer brackets minimize relative movement between inlet mixers 4 and restrainer brackets to minimize leakage or damage around slip joint 6.
FIG. 2 is a detailed view of related art slip joint 6 that exists between inlet mixer 4 and diffuser 2 of a BWR jet pump assembly. Bottom portion 4a of the inlet mixer 4 inserts into upper crown 2a of diffuser 2. A top edge of diffuser 2 includes one or more guide ears 2b to allow tolerances and easier connection between inlet mixer 4 and diffuser 2. The interface or mating between inlet mixer 4 and diffuser 2 is referred to as slip joint 6.
FIG. 3 is a cross-sectional view of related art slip joint 6 between inlet mixer 4 and diffuser 2 of a BWR jet pump assembly, showing internal relationships between components. Lowest distal end 4b of inlet mixer 4 rests in upper crown 2a of diffuser 2, to form slip joint 6. Inlet mixer FIV may occur in the slip joint 6 when tolerances between distal end 4b of inlet mixer 4 and upper crown 2a of diffuser 2 do not exactly match due to wear or improper machining. Leakage may occur at this interface due to both a poor fit and FIV, as fluid coolant leaks between lowest distal end 4b of inlet mixer 4 and upper crown 2a of diffuser 2 and out of the slip joint 6.